The present invention relates to an Alxe2x80x94Nixe2x80x94Fe alloy fin material for brazing that has excellent corrosion resistance, mechanical strength, and heat conductivity.
The majority of automotive heat exchangers is composed of Al and Al alloys, and is manufactured by brazing. Usually, a brazing material of Alxe2x80x94Si series is used for brazing, so that the brazing is carried out at a temperature as high as 600 xc2x0C. As shown in FIG. 1, for example, a heat exchanger, such as a radiator, has thin wall fins (2) machined in a corrugated form among plural flattened tubes (1) integrally built. Both ends of the flattened tubes (1) are opened respectively to a space formed by a header (3) and a tank (4), so that a high temperature refrigerant is transmitted from a space of the tank on one side through the flattened tubes (1) to a space of the tank (4) on the other side, thereby effecting heat exchange in a portion of the tubes (1) and the fins (2) and again circulating the resultant low temperature refrigerant.
In recent years, heat exchangers gradually become lightweight and smaller in size, thus necessitating enhancement of heat efficiency of the heat exchangers while enhancement of heat conductivity of the materials is desired. Especially, enhancement in heat conductivity of the fin materials is now being discussed and as a result a fin material of an alloy is proposed as a thermally conductive fin wherein the alloy composition are approached to pure aluminum. However, in case a fin is processed to a thin wall one, there arises a problem that the fin will be collapsed on assembling a heat exchanger or destroyed during the use as a heat exchanger, if the mechanical strength of fin is not sufficient. In case of a fin made of pure aluminum series alloy, the fin has a defect of lacking mechanical strength, so that addition of an alloying element such as Mn is effective for enhancing strength. Due to brazing heated up to about 600 xc2x0C. in the course of manufacturing a heat exchanger, however, there may be a problem that any element added to the alloy for enhancing mechanical strength will again become solid solution on heating for brazing to deteriorate promotion of heat conductivity.
As a fin material dissolving these problems, an Alxe2x80x94Sixe2x80x94Fe alloy to which Ni or Co has been added is proposed, which shows characteristics of excellent mechanical strength and heat conductivity (JP-A-7-216485 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application), JP-A-8-104934, etc.).
Among these fin materials, however, an aluminum alloy to which Fe exceeding 1.5% (% means wt %; the same will be applied hereinafter) has been added together with Ni permits generation of Alxe2x80x94Fexe2x80x94Ni series intermetallic compounds inside the fin material, these metals cause enhancement of mechanical strength and heat conductivity, but such the problem occurs that they also cause lowering corrosion resistance of the fin material itself. The fin material serves as a sacrificial corrosion-preventive material to protect tubes. However, if the corrosion resistance of the fin material itself is too low, the fin will be consumed in the early stages due to corrosion, failing to protect the tube for a long period of time.
The present invention is an aluminum alloy fin material for brazing which is composed of an aluminum alloy comprising more than 0.1 wt % but 3 wt % or less of Ni, more than 1.5 wt % but 2.2 wt % or less of Fe, and 1.2 wt % or less of Si, and at least one selected from the group consisting of 4 wt % or less of Zn, 0.3 wt % or less: of In, and 0.3 wt % or less of Sn, and further comprising, optionally, at least one selected from the group consisting of 3.0 wt % or less of Co, 0.3 wt % or less of Cr, 0.3 wt % or less of Zr, 0.3 wt % or less of Ti, 1 wt % or less of Cu, 0.3 wt % or less of Mn, and 1 wt % or less of Mg, and any unavoidable impurities with the balance being aluminum, wherein a ratio of a length in right angle direction to the rolling direction of an individual grain viewed from the sheet surface to a length of the grain in the parallel direction to the rolling direction (the grain length in the right angle direction/the grain length in the parallel directiØn) is 1/30 or less, an electric conductivity is 50% IACS or more but 55%IACS or less, and a tensile strength is 170 MPa or more but 280 MPa or less.
Other and further features, and advantages of the invention will appear more fully from the following description, take in connection with the accompanying drawing.